The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device having an integral built-in bipolar transistor and resistor, and a method of manufacturing the same.
A transistor and resistor are integrally built into some semiconductor device by using a wafer epitaxially grown on a substrate. An example of a transistor used in a semiconductor device of this type includes a heterojunction bipolar transistor (to be referred to as an HBT hereinafter) or any other types of bipolar transistor.
In the semiconductor device described above having the integral built-in HBT and resistor, for example, as shown in FIG. 11, a subcollector layer 301 is epitaxially grown on an insulating semiconductor substrate 300 made of GaAs, a collector layer 302, base layer 303, and emitter layer 304 are sequentially epitaxially grown on the subcollector layer 301, and a collector electrode 305, base electrode 306, and emitter electrode 307 are respectively formed on the subcollector layer 301, the base layer 303, and an emitter cap layer 308 on the emitter layer 304, respectively. With this arrangement, a heterojunction bipolar transistor (HBT) device 310 is formed on the semiconductor substrate 300.
In the semiconductor device shown in FIG. 11, an interlevel insulating film 311 is formed on the HBT device 310 described above, a metal resistor 313 is formed on the interlevel insulating film 311, and a pair of metal resistor electrodes 312 are formed on the metal resistor 313. In this manner, the HBT and resistor are integrally built into the semiconductor device.
In the semiconductor device having the arrangement shown in FIG. 11, since the interlevel insulating film 311 is arranged between the metal resistor 313 and subcollector layer 301, it serves as a capacitance component. The resistance of the metal resistor 313 is thus influenced by the capacitance component, and a net resistance cannot be obtained. Also, an extra manufacturing process is necessary for forming the metal resistor 313.
In a semiconductor device shown in FIG. 12 having a built-in HBT device, a subcollector layer 301b is formed adjacent to a subcollector layer 301 that forms an HBT, a resistor is formed by using the subcollector layer 301b, and a pair of metal resistor electrodes 312 are formed on this resistor 301b. Implantation regions 309 are formed for element isolation.
In the semiconductor device shown in FIG. 12, since the subcollector layer 301b is used as an access layer between the subcollector layer 301 and the HBT device, its resistance must be as low as possible, and accordingly the sheet resistance cannot be increased. When a high-resistance resistor is to be formed, the area of the subcollector layer 301b used as the resistor undesirably increases.
In a semiconductor device shown in FIG. 13, while a subcollector layer 301, collector layer 302, and base layer 303 that form an HBT are epitaxially grown, a subcollector layer 301b, collector layer 302b, and base layer 303b are formed by epitaxial growth. The base layer 303b located at the uppermost position of the HBT is used as a resistor, and a pair of resistor electrodes 312 are formed on this resistor 303b. Implantation regions 309 are formed for element isolation in the same manner as in FIG. 12.
In the semiconductor device shown in FIG. 13, when the collector layer 302b with a high resistance is used as a resistor, since the heavily doped collector layer 302b exists under the base layer 303b, the resistor comprised of the base layer 303b undesirably includes a capacitance component. Furthermore, since the base layer 303b has a thickness of as very small as 1,000 xc3x85 or less, the resistance of the resistor 303b varies.
It is, therefore, an object of the present invention to provide a semiconductor device in which a resistor with a desired resistance can be integrally built together with an HBT device without adversely affecting the characteristics of the HBT device, and a method of manufacturing the same.
In order to achieve the above object, according to an aspect of the present invention, there is provided a semiconductor device having an integral built-in bipolar transistor and resistor, the bipolar transistor being obtained by sequentially forming a subcollector layer, a collector layer, a base layer, and an emitter layer on an insulating semiconductor substrate, wherein the subcollector layer of the bipolar transistor is formed of two subcollector layers with different thicknesses, a resistor layer is formed at the same level as, among the subcollector layers, one layer away from the collector layer, from the same material as that of the subcollector away from the collector layer, and the resistor layer forms the resistor.